The pandemic COVID-19 was caused by a novel Coronavirus-2 (SARS-CoV-2) that infects humans through the binding of glycosylated SARS-CoV-2 spike 2 protein to the glycosylated ACE2 receptor. The spike 2 protein recognizes the N-terminal helices of the glycosylated metalloprotease domain in the human ACE2 receptor. To understand the susceptibility of animals for infection and transmission, we did sequence and structure-based molecular interaction analysis of 16 ACE2 receptors from different mammalian species with SARS-CoV-2 spike 2 receptor binding domain. Our comprehensive structure analysis revealed that the natural substitution of amino acid residues Gln24, His34, Phe40, Leu79 and Met82 in the N-terminal α1 and α2 helices of the ACE2 receptor results in loss of crucial network of hydrogen-bonded and hydrophobic interactions with receptor binding domain of SARS-CoV-2 spike protein. Another striking observation is the absence of N-glycosylation site Asn103 in all mammals and many species, lack more than one N-linked glycosylation site in the ACE2 receptor. Based on the loss of crucial interactions and the absence of N-linked glycosylation sites we categorized Felis catus, Equus caballus, Panthera tigris altaica, as highly susceptible while Oryctolagus cuniculus, Bos Tauras, Ovis aries and Capra hircus as moderately susceptible species for infection. Similarly, the E. asinus, Bubalus bubalis, Canis lupus familiaris, Ailuropoda melaleuca and Camelus dromedarius are categorized as low susceptible with Loxodonta Africana, Mus musculus, Sus scrofa and Rattus rattus as least susceptible species for SARS-CoV-2 infection.

The pandemic COVID-19 caused by a novel coronavirus SARS-CoV-2 spread worldwide as a new public health emergency. The SARS-CoV-2 infects humans by binding to glycosylated ACE2 receptor present in the inner lining of the lungs, heart, intestine and kidney. The COVID spike 2 protein recognizes the ACE2 receptor at the N-terminal helices of the metalloprotease domain. The residues Gln24, Thr27, Lys31, His34, Glu37, Asp38, Tyr41, Gln42 from helix α1; Leu79, Met82, Tyr83 from helix α2 and Gln325, Glu329, Asn330, Lys353 from loop connecting β4 and β5 strands form a concave surface surrounded by four glycosylation sites Asn53, Asn90, Asn103 and Asn322 form interactions with the spike protein. However, no significant data on the susceptibility of animals for infection or transmission. Therefore, we performed the comparative protein-protein docking analysis using the crystal structure of spike protein and homology models of the ACE2 receptor from 16 commonly found mammalian species to understand the potential mode of spike binding. Our comprehensive sequence and structure-based interaction analysis revealed the natural substitution of amino acid residues Gln24, His34, Phe40 and Met82 in the N-terminal α1 and α2 helices results in loss of crucial network of hydrogen-bonded and hydrophobic interactions with spike 2 RBD domain. Besides, the absence of N-linked glycosylation site Asn103 in other mammals further reduces the binding affinity between spike and ACE2 receptor. Hence, these changes explain the differences in the susceptibility and host pathogenesis in other mammalian species.

Background Radiolabeled RGD peptide can be used for noninvasive in vivo imaging of αvβ3 integrin receptors leading to early detection of tumor cells and hence improving the clinical outcomes. In the present study single vial kit based HYNIC RGD2 was radiolabeled with Tc-99m and evaluated in patients with breast carcinoma. Methods Radiolabeling was performed via bifunctional chelator method. Tc-99m 1110–2960 MBq (30–80 mCi) was added to the HYNIC-RGD2 vial. The reaction mixture was heated for 20 minutes at 100°C. After performing the quality checks, whole-body planar imaging was performed in 20 patients at 2–2.5 h post i.v. injection of 555–740 MBq (15–20 mCi) of the radiotracer. Results Radiolabeling yield of ≥98% was observed in all the formulations. Quality control tests indicated the suitability of radiopharmaceutical for intravenous administration. Physiological uptake of Tc-99m HYNIC-RGD2 was observed in the nasopharynx, salivary glands, liver, spleen, and intestine. Good uptake of radiotracer was observed in breast lesions of 18 patients. Two patients were observed to be negative. Increased uptake was also seen in metastatic sites in two patients and in lymph nodes in three patients. Scintigraphy findings were in corroboration with pathological observations. Conclusion The single vial cold kit based radiolabeling of Tc-99m HYNIC-RGD2 is facile leading to its easy availability. Tc-99m HYNIC-RGD2 is a promising radiopharmaceutical which can be used for the molecular imaging of angiogenesis in breast carcinoma patients.